Such length-measuring devices are used, in particular, in machine tools for measuring the position of a tool relative to a workpiece to be machined, in coordinate measuring machines for determining the position and dimensions of test objects, as well as in the semiconductor industry. In such devices, the scale is directly attached to a support, for example, the drive unit (e.g., a linear motor), or the scale is attached to a component driven by the drive unit. A scanning unit of the length-measuring device is stationarily disposed opposite the moving scale on a second object whose relative position with respect to the support is to be measured.
To create a fixed point of the scale with respect to the support, it is known to fix the scale to the support at one point such that it is stationary in the measurement direction.
In most cases, the scale and the support are composed of materials having different thermal expansion properties. The stationary fixation has to be implemented in such a way that no constraining forces will be exerted by the support on the scale in response to temperature changes.
In accordance with EP 0 264 801 A1, the stationary fixation of the scale is effected by means of a ball which is inserted in a V-groove of the scale, on the one hand, and in a V-groove of a holder, on the other hand, thereby creating an interlocking fit. The scale is urged by a spring against the ball, so that the interlocking fit is ensured between the ball and the scale, on the one hand, and between the ball and the holder, on the other hand.
In accordance with WO 02/27265 A2, the stationary fixation with respect to the measurement direction is effected by means of a mounting element having a first fastening portion by which it is stationarily attached to the scale and a second fastening portion by which it is attached to a support. Provided between the first fastening portion and the second fastening portion is a roller bearing which allows displacement of the scale relative to the support in a direction perpendicular to the measurement direction.